Poly(Lactic-Co-Glycolic Acid) Microparticles for the Delivery of Model Drug Compounds for Applications in Vascular Tissue Engineering.

INTRODUCTION: Localized delivery of angiogenesis-promoting factors such as small molecules, nucleic acids, peptides, and proteins to promote the repair and regeneration of damaged tissues remains a challenge in vascular tissue engineering. Current delivery methods such as direct administration of therapeutics can fail to maintain the necessary sustained release profile and often rely on supraphysiologic doses to achieve the desired therapeutic effect. By implementing a microparticle delivery system, localized delivery can be coupled with sustained and controlled release to mitigate the risks involved with the high dosages currently required from direct therapeutic administration. METHODS: For this purpose, poly(lactic-co-glycolic acid) (PLGA) microparticles were fabricated via anti-solvent microencapsulation and the loading, release, and delivery of model angiogenic molecules, specifically a small molecule, nucleic acid, and protein, were assessed in vitro using microvascular fragments (MVFs). RESULTS: The microencapsulation approach utilized enabled rapid spherical particle formation and encapsulation of model drugs of different sizes, all in one method. The addition of a fibrin scaffold, required for the culture of the MVFs, reduced the initial burst of model drugs observed in release profiles from PLGA alone. Lastly, in vitro studies using MVFs demonstrated that higher concentrations of microparticles led to greater co-localization of the model therapeutic (miRNA) with MVFs, which is vital for targeted delivery methods. It was also found that the biodistribution of miRNA using the delivered microparticle system was enhanced compared to direct administration. CONCLUSION: Overall, PLGA microparticles, formulated and loaded with model therapeutic compounds in one step, resulted in improved biodistribution in a model of the vasculature leading to a future in translational revascularization.

K+ontrol rapidly and efficiently reduces potassium in donor blood during ex vivo circulation.

BACKGROUND: Patients with kidney failure are at risk for lethal complications from hyperkalemia. Resuscitation, medications, and hemodialysis are used to mitigate increased potassium (K+) levels in circulating blood; however, these approaches may not always be readily available or effective, especially in a resource limited environment. We tested a sorbent cartridge (KC, K+ontrol CytoSorbents Medical Inc., Monmouth Junction, New Jersey) which contains a resin adsorber for K+. The objective of this study was to test the utility of KC in an ex vivo circulation system. We hypothesized that KC reduces K+ levels in extracorporeal circulation of donor swine whole blood infused with KCl. METHODS: A six-hour circulation study was carried out using KC, a NxStage (NxStage Medical, Inc., Lawrence, MA) membrane, blood bag containing heparinized whole blood with KCl infusion, 3/16-inch ID tubing, a peristaltic pump, and flow sensors. The NxStage permeate line was connected back to the main circuit in the Control group (n = 6), creating a recirculation loop. For KC group (n = 6), KC was added to the recirculation loop, and a continuous infusion of KCl at 10 mEq/hour was administered for two hours. Blood samples were acquired at baseline and every hour for 6 h. RESULTS: In the control group, K+ levels remained at ∼9 mmol/L; 9.1 ± 0.4 mmol/L at 6 h. In the KC group, significant decreases in K+ at hour 1 (4.3 ± 0.3 mmol/L) and were sustained for the experiment duration equilibrating at 4.6 ± 0.4 mmol/L after 6 h (p = 0.042). Main loop blood flow was maintained under 400 mL/min; recirculation loop flow varied between 60 and 70 mL/min in the control group and 45-55 mL/min in the KC group. Decreases in recirculation loop flow in KC group required 7% increase of pump RPM. CONCLUSIONS: During ex-vivo extracorporeal circulation using donor swine blood, KC removed approximately 50% of K+, normalizing circulating levels.

Development of bioinks for 3D printing microporous, sintered calcium phosphate scaffolds.

Beta-tricalcium phosphate (ß-TCP)-based bioinks were developed to support direct-ink 3D printing-based manufacturing of macroporous scaffolds. Binding of the gelatin:ß-TCP ink compositions was optimized by adding carboxymethylcellulose (CMC) to maximize the ß-TCP content while maintaining printability. Post-sintering, the gelatin:ß-TCP:CMC inks resulted in uniform grain size, uniform shrinkage of the printed structure, and included microporosity within the ceramic. The mechanical properties of the inks improved with increasing ß-TCP content. The gelatin:ß-TCP:CMC ink (25:75 gelatin:ß-TCP and 3% CMC) optimized for mechanical strength was used to 3D print several architectures of macroporous scaffolds by varying the print nozzle tip diameter and pore spacing during the 3D printing process (compressive strength of 13.1 ± 2.51 MPa and elastic modulus of 696 ± 108 MPa was achieved). The sintered, macroporous ß-TCP scaffolds demonstrated both high porosity and pore size but retained mechanical strength and stiffness compared to macroporous, calcium phosphate ceramic scaffolds manufactured using alternative methods. The high interconnected porosity (45-60%) and fluid conductance (between 1.04 ×10-9 and 2.27 × 10-9 m4s/kg) of the ß-TCP scaffolds tested, and the ability to finely tune the architecture using 3D printing, resulted in the development of novel bioink formulations and made available a versatile manufacturing process with broad applicability in producing substrates suitable for biomedical applications.

A Novel Secretome Biotherapeutic Influences Regeneration in Critical Size Bone Defects.

Severe traumatic injuries often result in critical size bone defects, which are unable to heal without treatment. Autologous grafting is the standard of care but requires additional surgeries for graft procurement. Amnion-derived multipotent progenitor cells release a secretome of biomolecules identified as integral to the process of bone regeneration and angiogenesis. This secretome is currently under development as a biotherapeutic. The efficacy of this secretome biotherapeutic was evaluated in vitro on the proliferation and migration of mesenchymal stem cells and osteoprogenitor cells as well as in vivo using a critical size rat calvarial defect model. The secretome biotherapeutic was loaded onto a collagen scaffold and placed into the defect, which was allowed to heal for 4 and 12 weeks. The secretome biotherapeutic enhanced the proliferation and migration of mesenchymal stem cells and proliferation of osteoprogenitor cells. Further, the secretome biotherapeutic improved new bone volume and connectivity by 12 weeks and significantly improved angiogenesis at 4 weeks and bone density at 4 and 12 weeks with no deleterious effects. The improvement in new bone volume, connectivity, and angiogenesis suggests that the secretome biotherapeutic has beneficial effects for bone healing and a higher dose of the secretome biotherapeutic may further improve regeneration.

Evaluation of Amniotic Multipotential Tissue Matrix to Augment Healing of Demineralized Bone Matrix in an Animal Calvarial Model.

Amniotic multipotential tissue matrix (AmnioMTM) is a membrane material derived from placental tissues and rich in growth factors that have been reported to have potential in healing bone. This study hypothesized that demineralized bone matrix (DBM) supplemented with AmnioMTM would accelerate healing and bone formation as compared with DBM alone in a critical size (10 mm) rat calvarial bone defect model. Five DBM grafts and 5 DBM supplemented with AmnioMTM grafts were implanted in a 10-mm critical sized defect in 10 rats (1 implant per rat). After 4 weeks, animals were euthanized and defects evaluated by microCT and histology. There were no statistical differences in microCT data for mineral density, percent bone fill, or bone surface to volume ratios between groups, though the bone surface to volume ratio for the amnio-supplemented group suggested increased osteoid activity as compared with the DBM alone group. Histological data also indicated active osteoid activity and induced bone formation in the center of defects implanted with AmnioMTM supplemented graft as compared with DBM graft alone suggesting some potential osteoinductive potential. However, there was no significant difference at the mean percent of newly mineralized bone in the DBM group defect as compared with the AmnioMTM supplemented graft material. These data suggest that while bone formation was not increased at this early time point, the increased osteoid activity and the induction of new bone in the middle of the defect by the AmnioMTM indicates that further study is needed to assess its potential benefit to bone healing and regeneration.

Quality of bone healing: perspectives and assessment techniques.

Bone regeneration and healing is an area of extensive research providing an ever-expanding set of not only therapeutic solutions for surgeons but also diagnostic tools. Multiple factors such as an ideal graft, the appropriate biochemical and mechanical wound environment, and viable cell populations are essential components in promoting healing. While bony tissue performs many functions, critical is mechanical strength, followed closely by structure. Many tools are available to evaluate bone quality in terms of quantity, structure, and strength; the purpose of this article is to identify the factors that can be evaluated and the advantages and disadvantages of each in assessing the quality of bone healing in both preclinical research and clinical settings.

Differentiated adipose-derived stem cell cocultures for bone regeneration in polymer scaffolds in vivo.

Critical-sized bone defects can lead to significant morbidity, and interventions are limited by the availability and donor-site morbidity of bone grafts. Polymer scaffolds seeded with cells have been explored to replace bone grafts. Adipose-derived stem cells have shown great promise for vascularization and osteogenesis of these constructs, and cocultures of differentiated stem cells are being explored to augment vessel and bone formation. Adipose-derived stem cells were differentiated into endothelial cells and osteoblasts, and in vitro studies showed increased proliferation of cocultured cells compared with undifferentiated adipose-derived stem cells and monocultures of endothelial cells and osteoblasts. The cells were seeded into polylactic acid gas-plasma-treated scaffolds as cocultures and monocultures and then implanted into critical-sized rat calvarial defects. The cocultures were in a 1:1 osteoblast to endothelial cell ratio. The increase in proliferation seen by the cocultured cells in vitro did not translate to increased vascularization and osteogenesis in vivo. In vivo, there were trends of increased vascularization in the endothelial cell group and increased osteogenesis in the osteoblast and endothelial monoculture groups, but no increase was seen in the coculture group compared with the undifferentiated adipose-derived stem cells. Endothelial cells enhance vascularization and osteoblast and endothelial cell monocultures enhance bone formation in the polymer scaffold. Predifferentiation of adipose-derived stem cells is promising for improving vascularization and osteogenesis in polymer scaffolds but requires future evaluation of coculture ratios to fully characterize this response.

Changes in vocal fold gene expression and histology after injection augmentation in a recurrent laryngeal nerve injury model.

OBJECTIVE: To investigate changes in neuroregenerative pathways with vocal fold denervation in response to vocal fold augmentation. METHODS: Eighteen Yorkshire crossbreed swine underwent left recurrent laryngeal nerve transection, followed by observation or augmentation with carboxymethylcellulose or calcium hydroxyapatite at two weeks. Polymerase chain reaction expression of genes regulating muscle growth (MyoD1, MyoG and FoxO1) and atrophy (FBXO32) were analysed at 4 and 12 weeks post-injection. Thyroarytenoid neuromuscular junction density was quantified using immunohistochemistry. RESULTS: Denervated vocal folds demonstrated reduced expression of MyoD1, MyoG, FoxO1 and FBXO32, but overexpression after augmentation. Healthy vocal folds showed increased early and late MyoD1, MyoG, FoxO1 and FBXO32 expression in all animals. Neuromuscular junction density had a slower decline in augmented compared to untreated denervated vocal folds, and was significantly reduced in healthy vocal folds contralateral to augmentation. CONCLUSION: Injection augmentation may slow neuromuscular degeneration pathways in denervated vocal folds and reduce compensatory remodelling in contralateral healthy vocal folds.

Connexin hemichannels drive lactation-induced osteocyte acidification and perilacunar-canalicular remodeling.

The maternal skeleton experiences significant bone loss during lactation, followed by rapid restoration post weaning. Parathyroid-related protein (PTHrP)-induced acidification of the perilacunar matrix by osteocytes is crucial in this process, yet its mechanism remains unclear. Here, we identify Cx43 hemichannels (HCs) as key mediators of osteocyte acidification and perilacunar-canalicular remodeling (PLR). Utilizing transgenic mouse models expressing dominant-negative Cx43 mutants, we show that mice with impaired Cx43 HCs exhibit attenuated lactation-induced responses compared to wild-type and only gap junction-impaired groups, including lacunar enlargement, upregulation of PLR genes, and bone loss with compromised mechanical properties. Furthermore, inhibition of HCs by a Cx43 antibody blunts PTHrP-induced calcium influx and protein kinase A activation, followed by impaired osteocyte acidification. Additionally, impeded HCs suppress bone recovery during the post-lactation period. Our findings highlight the pivotal role of Cx43 HCs in orchestrating dynamic bone changes during lactation and recovery by regulating acidification and remodeling enzyme expression.

Electrospun composite-coated endotracheal tubes with controlled siRNA and drug delivery to lubricate and minimize upper airway injury.

Endotracheal Tubes (ETTs) maintain and secure a patent airway; however, prolonged intubation often results in unintended injury to the mucosal epithelium and inflammatory sequelae which complicate recovery. ETT design and materials used have yet to adapt to address intubation associated complications. In this study, a composite coating of electrospun polycaprolactone (PCL) fibers embedded in a four-arm polyethylene glycol acrylate matrix (4APEGA) is developed to transform the ETT from a mechanical device to a dual-purpose device capable of delivering multiple therapeutics while preserving coating integrity. Further, the composite coating system (PCL-4APEGA) is capable of sustained delivery of dexamethasone from the PCL phase and small interfering RNA (siRNA) containing polyplexes from the 4APEGA phase. The siRNA is released rapidly and targets smad3 for immediate reduction in pro-fibrotic transforming growth factor-beta 1 (TGFϐ1) signaling in the upper airway mucosa as well as suppressing long-term sequelae in inflammation from prolonged intubation. A bioreactor was used to study mucosal adhesion to the composite PCL-4APEGA coated ETTs and investigate continued mucus secretory function in ex vivo epithelial samples. The addition of the 4APEGA coating and siRNA delivery to the dexamethasone delivery was then evaluated in a swine model of intubation injury and observed to restore mechanical function of the vocal folds and maintain epithelial thickness when observed over 14 days of intubation. This study demonstrated that increase in surface lubrication paired with surface stiffness reduction significantly decreased fibrotic behavior while reducing epithelial adhesion and abrasion.

Endotracheal tubes with dexamethasone eluting electrospun coating improve tissue mechanical function after upper airway injury.

Corticosteroid-eluting endotracheal tubes (ETTs) were developed and employed in a swine laryngotracheal injury model to maintain airway patency and provide localized drug delivery to inhibit fibrotic scarring. Polycaprolactone (PCL) fibers with or without dexamethasone were electrospun onto the ETT surface PCL-only coated ETTs and placed in native airways of 18 Yorkshire swine. Regular and dexamethasone-PCL coated ETTs were placed in airways of another 18 swine injured by inner laryngeal mucosal abrasion. All groups were evaluated after 3, 7 and 14 days (n = 3/treatment/time). Larynges were bisected and localized stiffness determined by normal indentation, then sequentially matched with histological assessment. In the native airway, tissue stiffness with PCL-only ETT placement increased significantly from 3 to 7 days (p = 0.0016) and 3 to 14 days (p < 0.0001) while dexamethasone-PCL ETT placement resulted in stiffness decreasing from 7 to 14 days (p = 0.031). In the injured airway, localized stiffness at 14 days was significantly greater after regular ETT placement (23.1 ± 0.725 N/m) versus dexamethasone-PCL ETTs (17.10 ± 0.930 N/m, p < 0.0001). Dexamethasone-loaded ETTs were found to reduce laryngotracheal tissue stiffening after simulated intubation injury compared to regular ETTs, supported by a trend of reduced collagen in the basement membrane in injured swine over time. Findings suggest localized corticosteroid delivery allows for tissue stiffness control and potential use as an approach for prevention and treatment of scarring caused by intubation injury.

Impact of PEG sensitization on the efficacy of PEG hydrogel-mediated tissue engineering.

While poly(ethylene glycol) (PEG) hydrogels are generally regarded as biologically inert blank slates, concerns over PEG immunogenicity are growing, and the implications for tissue engineering are unknown. Here, we investigate these implications by immunizing mice against PEG to stimulate anti-PEG antibody production and evaluating bone defect regeneration after treatment with bone morphogenetic protein-2-loaded PEG hydrogels. Quantitative analysis reveals that PEG sensitization increases bone formation compared to naive controls, whereas histological analysis shows that PEG sensitization induces an abnormally porous bone morphology at the defect site, particularly in males. Furthermore, immune cell recruitment is higher in PEG-sensitized mice administered the PEG-based treatment than their naive counterparts. Interestingly, naive controls that were administered a PEG-based treatment also develop anti-PEG antibodies. Sex differences in bone formation and immune cell recruitment are also apparent. Overall, these findings indicate that anti-PEG immune responses can impact tissue engineering efficacy and highlight the need for further investigation.

Effect of continuous local dexamethasone on tissue biomechanics and histology after inhalational burn in a preclinical model.

Objective: Inhalational burns frequently lead to dysphonia and airway stenosis. We hypothesize local dexamethasone delivery via a novel drug-eluting electrospun polymer-mesh endotracheal tube (ETT) reduces biomechanical and histologic changes in the vocal folds in inhalational burn. Methods: Dexamethasone-loaded polymer mesh was electrospun onto ETTs trimmed to transglottic endolaryngeal segments and secured in nine Yorkshire Crossbreed swine with directed 150°C inhalation burns. Uncoated ETTs were implanted in nine additional swine with identical burns. ETT segments were maintained for 3 and 7 days. Vocal fold (VF) structural stiffness was measured using automated-indentation mapping and compared across groups and to four uninjured controls, and matched histologic assessment performed. Statistical analysis was conducted using two-way ANOVA with Tukey's post hoc test and Wilcoxon rank-sum test. Results: VF stiffness after burn decreased with longer intubation, from 19.4 (7.6) mN/mm at 3 days to 11.3 (5.2) mN/mm at 7 days (p < .0001). Stiffness similarly decreased with local dexamethasone, from 25.9 (17.2) mN/mm at 3 days to 18.1 (13.0) mN/mm at 7 days (p < .0001). VF stiffness in the dexamethasone group was increased compared to tissues without local dexamethasone (p = .0002), and all groups with ETT placement had higher tissue stiffness at 3 days (p < .001). No significant change in histologic evidence of epithelial ulceration or fibrosis was noted, while an increased degree of inflammation was noted in the dexamethasone group (p = .04). Conclusion: Local dexamethasone delivery increases VF stiffness and degree of inflammation compared to uncoated ETTs in an acute laryngeal burn model, reflected in early biomechanical and histologic changes in an inhalational burn model.

Connexin hemichannels with prostaglandin release in anabolic function of bone to mechanical loading.

Mechanical stimulation, such as physical exercise, is essential for bone formation and health. Here, we demonstrate the critical role of osteocytic Cx43 hemichannels in anabolic function of bone in response to mechanical loading. Two transgenic mouse models, R76W and Δ130-136, expressing dominant-negative Cx43 mutants in osteocytes were adopted. Mechanical loading of tibial bone increased cortical bone mass and mechanical properties in wild-type and gap junction-impaired R76W mice through increased PGE2, endosteal osteoblast activity, and decreased sclerostin. These anabolic responses were impeded in gap junction/hemichannel-impaired Δ130-136 mice and accompanied by increased endosteal osteoclast activity. Specific inhibition of Cx43 hemichannels by Cx43(M1) antibody suppressed PGE2 secretion and impeded loading-induced endosteal osteoblast activity, bone formation and anabolic gene expression. PGE2 administration rescued the osteogenic response to mechanical loading impeded by impaired hemichannels. Together, osteocytic Cx43 hemichannels could be a potential new therapeutic target for treating bone loss and osteoporosis.

Augmentation and vocal fold biomechanics in a recurrent laryngeal nerve injury model.

Objectives/hypothesis: Composite vocal fold (VF) biomechanical data are lacking for augmentation after recurrent laryngeal nerve (RLN) injury. We hypothesize resulting atrophy decreases VF stiffness and augmentation restores native VF biomechanics. Methods: Sixteen Yorkshire Crossbreed swine underwent left RLN transection and were observed or underwent carboxymethylcellulose (CMC) or calcium hydroxyapatite (CaHa) augmentation at 2 weeks. Biomechanical measurements (structural stiffness, displacement, and maximum load) were measured at 4 or 12 weeks. Thyroarytenoid (TA) muscle cross-sectional area was quantified and compared with two-way ANOVA with Tukey's post hoc test. Results: After 4 weeks, right greater than left structural stiffness (mean ± SE) was observed (49.6 ± 0.003 vs. 28.4 ± 0.002 mN/mm), left greater than right displacement at 6.3 mN (0.54 ± 0.01 vs. 0.46 ± 0.01 mm, p < .01) was identified, and right greater than left maximum load (72.3 ± 0.005 vs. 40.8 ± 0.003 mN) was recorded. TA muscle atrophy in the injured group without augmentations was significant compared to the noninjured side, and muscle atrophy was seen at overall muscle area and individual muscle bundles. CMC augmentation appears to maintain TA muscle structure in the first 4 weeks with atrophy present at 12 weeks. Conclusions: VF biomechanical properties match TA muscle atrophy in this model, and both CMC and CaHa injection demonstrated improved biomechanical properties and slower TA atrophy compared to the uninjured side. Taken together, these data provide a quantifiable biomechanical basis for early injection laryngoplasty to improve dysphonia and potentially improve healing in reversible unilateral vocal fold atrophy. Level of evidence: N/A.

Spatial Recombinant Human Bone Morphogenetic Protein 2 Delivery from Hydroxyapatite Scaffolds Sustains Bone Regeneration in Rabbit Radius.

Regenerating large bone defects requires a multifaceted approach combining optimal scaffold designs with appropriate growth factor delivery. Supraphysiological doses of recombinant human bone morphogenetic protein 2 (rhBMP2), typically used for the regeneration of large bone defects clinically in conjunction with an acellular collagen sponge (ACS), have resulted in many complications. In this study, we develop a hydroxyapatite/collagen I (HA/Col) scaffold to improve the mechanical properties of the HA scaffolds, while maintaining open connected porosity. Varying rhBMP2 dosages were then delivered from a collagenous periosteal membrane and paired with HA or HA/Col scaffolds to treat critical-sized (15 mm) diaphyseal radial defect in New Zealand white rabbits. The groups examined were ACS +76 µg rhBMP2 (clinically used INFUSE dosage), HA +76 µg rhBMP2, HA +15 µg rhBMP2, HA/Col +15 µg rhBMP2, and HA/Col +15 µg rhBMP2 + bone marrow-derived stromal cells (bMSCs). After 8 weeks of implantation, all regenerated bones were evaluated using microcomputed tomography, histology, histomorphometry, and torsional testing. It was observed that the bone volume regenerated in the HA/Col +15 µg rhBMP2 group was significantly higher than that in the groups with 76 µg rhBMP2. The same scaffold and growth factor combination resulted in the highest bone mineral density of the regenerated bone, and the most bone apposition on the scaffold surface. Both the HA and HA/Col scaffolds paired with 15 µg rhBMP2 had sustained ingrowth of the mineralization front after 2 weeks compared to the groups with 76 µg rhBMP2, which had far greater mineralization in the first 2 weeks after implantation. Complete bridging of the defect site and no significant difference in torsional strength, stiffness, or angle at failure were observed across all groups. No benefit of additional bMSC seeding was observed on any of the quantified metrics, while bone-implant apposition was reduced in the cell-seeded group. This study demonstrated that the controlled spatial delivery of rhBMP2 at the periosteum at significantly lower doses can be used as a strategy to improve bone regeneration around space maintaining scaffolds. Tweet Inside-out or outside-in: growth factors delivered from the outside of porous mineral-collagen scaffolds, maintain strength and regrow bone better in a rabbit study. Twitter handle for senior author (@Guda_Lab) and sponsoring institution (@UTSA) Impact Statement This study provides insights on bone regeneration in the presence of spatially controlled delivery of recombinant human bone morphogenetic protein 2 (rhBMP2) from porous hydroxyapatite scaffolds coated with collagen I films. Using critical-sized defects created in the radial diaphysis of skeletally mature New Zealand White rabbits, microcomputed tomography and histomorphometry indicated significantly higher bone regeneration, bone mineral density, and bone-implant contact, as well as sustained regeneration over longer durations with lower dosage of rhBMP2 delivered periosteally.

Osteocytes regulate bone anabolic response to mechanical loading in male mice via activation of integrin α5.

Physical mechanical stimulation can maintain and even increase bone mass. Here, we report an important role of osteocytic integrin α5 in regulating the anabolic response of bone to mechanical loading using an Itga5 conditional gene knockout (cKO) mouse model. Integrin α5 gene deletion increased apoptotic osteocytes and reduced cortical anabolic responses to tibial compression including decreased endosteal osteoblasts and bone formation, and increased endosteal osteoclasts and bone resorption, contributing to the decreased bone area fraction and biomechanical properties, leading to an enlarged bone marrow area in cKO mice. Similar disruption of anabolic responses to mechanical loading was also detected in cKO trabecular bone. Moreover, integrin α5 deficiency impeded load-induced Cx43 hemichannel opening, and production and release of PGE2, an anabolic factor, resulting in attenuated effects of the loading on catabolic sclerostin (SOST) reduction and anabolic ß-catenin increase. Together, this study shows an indispensable role of integrin α5 in osteocytes in the anabolic action of mechanical loading on skeletal tissue through activation of hemichannels and PGE2-evoked gene expression. Integrin α5 could act as a potential new therapeutic target for bone loss, especially in the elderly population with impeded mechanical sensitivity.

In vivo performance of bilayer hydroxyapatite scaffolds for bone tissue regeneration in the rabbit radius.

The objective of this study was to investigate the in vivo biomechanical performance of bone defects implanted with novel bilayer hydroxyapatite (HAp) scaffolds that mimic the cortical and cancellous organization of bone. The scaffolds maintained architectural continuity in a rabbit radius segmental defect model and were compared to an untreated defect group (negative control) and autologous bone grafts (positive control). Micro-CT evaluations indicated total bone and scaffold volume in the experimental group was significantly greater than the defect group but lesser than the autologous bone graft treatment. The flexural toughness of the scaffold and the autograft groups was significantly greater than the flexural toughness of the defect group. Interestingly, the absolute density of the bone mineral as well as calcium to phosphorus (Ca/P) ratio in that mineral for the scaffold and autograft contralateral bones was significantly higher than those for the defect contralaterals suggesting that the scaffolds contributed to calcium homeostasis. It was concluded from this study that new bone regenerated in the bilayer HAp scaffolds was comparable to the empty defects and while the HAp scaffolds provided significant increase in modulus when compared to empty defect and their flexural toughness was comparable to autografts after 8 weeks of implantation.

Electrically Stimulated Tunable Drug Delivery From Polypyrrole-Coated Polyvinylidene Fluoride.

Electrical stimulus-responsive drug delivery from conducting polymers such as polypyrrole (PPy) has been limited by lack of versatile polymerization techniques and limitations in drug-loading strategies. In the present study, we report an in-situ chemical polymerization technique for incorporation of biotin, as the doping agent, to establish electrosensitive drug release from PPy-coated substrates. Aligned electrospun polyvinylidene fluoride (PVDF) fibers were used as a substrate for the PPy-coating and basic fibroblast growth factor and nerve growth factor were the model growth factors demonstrated for potential applications in musculoskeletal tissue regeneration. It was observed that 18-h of continuous polymerization produced an optimal coating of PPy on the surface of the PVDF electrospun fibers with significantly increased hydrophilicity and no substantial changes observed in fiber orientation or individual fiber thickness. This PPy-PVDF system was used as the platform for loading the aforementioned growth factors, using streptavidin as the drug-complex carrier. The release profile of incorporated biotinylated growth factors exhibited electrosensitive release behavior while the PPy-PVDF complex proved stable for a period of 14 days and suitable as a stimulus responsive drug delivery depot. Critically, the growth factors retained bioactivity after release. In conclusion, the present study established a systematic methodology to prepare PPy coated systems with electrosensitive drug release capabilities which can potentially be used to encourage targeted tissue regeneration and other biomedical applications.

Development of a Bioinspired, Self-Adhering, and Drug-Eluting Laryngotracheal Patch.

OBJECTIVES/HYPOTHESIS: Novel laryngotracheal wound coverage devices are limited by complex anatomy, smooth surfaces, and dynamic pressure changes and airflow during breathing. We hypothesize that a bioinspired mucoadhesive patch mimicking how geckos climb smooth surfaces will permit sutureless wound coverage and also allow drug delivery. STUDY DESIGN: ex-vivo. METHODS: Polycaprolactone (PCL) fibers were electrospun onto a substrate and polyethylene glycol (PEG) - acrylate flocks in varying densities were deposited to create a composite patch. Sample topography was assessed with laser profilometry, material stiffness with biaxial mechanical testing, and mucoadhesive testing determined cohesive material failure on porcine tracheal tissue. Degradation rate was measured over 21 days in vitro along with dexamethasone drug release profiles. Material handleability was evaluated via suture retention and in cadaveric larynges. RESULTS: Increased flocking density was inversely related to cohesive failure in mucoadhesive testing, with a flocking density of PCL-PEG-2XFLK increasing failure strength to 6880 ± 1810 Pa compared to 3028 ± 791 in PCL-PEG-4XFLK density and 1182 ± 262 in PCL-PEG-6XFLK density. The PCL-PEG-2XFLK specimens had a higher failure strength than PCL alone (1404 ± 545 Pa) or PCL-PEG (2732 ± 840). Flocking progressively reduced composite stiffness from 1347 ± 15 to 763 ± 21 N/m. Degradation increased from 12% at 7 days to 16% after 10 days and 20% after 21 days. Cumulative dexamethasone release at 0.4 mg/cm2 concentration was maintained over 21 days. Optimized PCL-PEG-2XFLK density flocked patches were easy to maneuver endoscopically in laryngeal evaluation. CONCLUSIONS: This novel, sutureless, patch is a mucoadhesive platform suitable to laryngeal and tracheal anatomy with drug delivery capability. LEVEL OF EVIDENCE: NA Laryngoscope, 131:1958-1966, 2021.